Gasoline regulations are increasingly creating a need to treat various refinery streams and products, for example, cracked gasoline blending material, including coker naphtha and gasoline from a catalytic cracking unit, to remove undesirable sulfur that is contained in such refinery streams and products.
One means by which sulfur may be removed from hydrocarbon streams that contain olefin compounds is through the use of various known catalytic hydroprocessing methods. A problem with the use of many conventional catalytic hydroprocessing methods is that they typically tend to hydrogenate the olefin compounds as well as the sulfur compounds contained in the hydrocarbon feed stream being treated. When the hydrocarbon feed stream is to be used as a gasoline-blending component, usually the presence of the olefins is desirable due to their relatively high-octane values and octane contribution to the gasoline pool.
Cracked gasoline blending material typically contains high concentrations of high-octane olefin compounds as well as concentrations of sulfur compounds. It is desirable to be able to catalytically desulfurize the cracked gasoline blending materials with a minimum of hydrogenation of the olefins contained in them. Disclosed in the prior art are many types of hydroprocessing catalysts and processes, and the prior art even discloses processes for the selective hydrodesulfurization of olefin containing hydrocarbon feedstocks.
U.S. Pat. No. 5,266,188 is one patent that discloses a process for the selective hydrotreating of a cracked naphtha using a catalyst comprising a Group VIB metal component, a Group VIII metal component, a magnesium component, and an alkali metal component. The Group VIB metal component is present in the catalyst in an amount in the range of from about 4 wt % to about 20 wt %, and the Group VIII metal component is present in the range of from about 0.5 wt % to about 10 wt %, both calculated as oxides and based on the total catalyst weight. The preferred Group VIB metals are molybdenum and tungsten with molybdenum being preferred among these, and the preferred Group VIII metals are cobalt and nickel with cobalt being preferred among these.
U.S. Pat. No. 5,686,375 discloses a hydroprocessing catalyst that contains an overlayer of a Group VIB metal (preferably molybdenum) component on a support comprising an underbedded Group VIII metal (preferably nickel) component combined with a porous refractory oxide. The catalyst typically contains greater than 3.0, preferably greater than 4.0, and most preferably greater than 4.5 weight percent of Group VIII metal component (calculated as the monoxide) and greater than 10, and preferably greater than 17 weight percent of Group VIB metal component (calculated as the trioxide). A preferred catalyst is essentially free of supported metal components other than molybdenum and underbedded nickel. A most highly preferred embodiment of the catalyst contains above 3 weight percent of nickel components, including underbedded nickel components encompassing at least 4.5 weight percent of the support. The catalyst is used in hydroprocessing methods such as desulfurization and denitrogenation, but there is no indication that the process is selective to desulfurization.
U.S. Patent Publication No. 2003/0183556 A1 discloses a process for the selective hydrodesulfurization of naphtha which uses a preferred catalyst that comprises a MoO3 concentration of about 1 to 10 wt. %, preferably about 2 to 8 wt. %, and more preferably about 4 to 6 wt. %, based on the total weight of the catalyst, and a CoO concentration of about 0.1 to 5 wt. %, preferably about 0.5 to 4 wt. %, and more preferably about 1 to 3 wt. % based on the total weight of the catalyst. The process includes blending a cracked naphtha feedstream that contains sulfur with a substantially olefin free naphtha feedstream and selectively hydrodesulfurizing the blend in the presence of a hydrodesulfurizing catalyst.
U.S. Pat. Nos. 6,589,418; 6,126,814; and 6,013,598 discloses processes for the selective hydrodesulfurization of an olefin-containing naphtha feedstock that use catalysts that are similar to those disclosed in U.S. Patent Publication No. 2003/0183556.
U.S. Pat. No. 5,286,373 discloses a process for selectively hydrodesulfurizing a naphtha feedstock having a high olefin content by using a deactivated hydrotreating catalyst.
The deactivated hydrotreating catalyst is a hydrotreating catalyst that has been deactivated by use or by other means, and it generally contains deposits of coke. The hydrotreating catalyst typically includes Group VI and Group VIII metals, provided on a porous support. The preferred Group VI metals include chromium, molybdenum and tungsten, and the preferred Group VIII metals include cobalt and nickel. Additional metals or other elements can be present, such as phosphorus, fluorine, titanium, boron and the like. The particularly preferred metals include cobalt and molybdenum.
As may be seen from the above review of some of the prior art there is great interest in the development of processes that provide for the selective catalytic hydrodesulfurization of sulfur-containing naphtha or hydrocarbon feedstocks that boil in the gasoline boiling range and contain high olefin contents. By the selective hydrodesulfurization of the sulfur without significant simultaneous hydrogenation of the olefins the loss in octane of the feedstock may be minimized; since, as noted above, olefins tend to be high-octane components of certain gasoline blending components.
An objective of the present invention therefore is to provide a catalyst and process for selectively desulfurizing a sulfur-containing hydrocarbon feedstock that has high olefin content.